Re: New switch/case idea
- Posted by jeremy (admin) Apr 06, 2009
- 1664 views
I am failing to detect the logic in this discussion.
switch x -- x = 1, let's say case 1 : print "one" case 2 : print "two"
Why on earth would anyone EVER expect this to print "onetwo", when x = 1?
Can anyone show me a justification for this? Or any example where some other construct wouldn't do the same thing in a clearer way? Or have I simply misread some posts and don't understand?
Irv, that is the way switch is designed, for many valid reasons. We use switch galore w/your exact situation in Euphoria's internal code (both C and Euphoria).
The problem most new people have with switch is they think of it as if/elsif/elsif/else. It is not. It's more like a goto. Once a case matches, execution of the switch block continues w/o regard for any other case statement. Case statements are just labels, basically, that is used for jumping into the switch at a given location.
A switch with fallthru is not a if/elsif/else statement. Here is a valid example:
switch op with fallthru do case RETURNT then opRETURNT() break case RHS_SLICE then opRHS_SLICE() break case RHS_SUBS then case RHS_SUBS_CHECK then case RHS_SUBS_I then opRHS_SUBS() break case RIGHT_BRACE_2 then opRIGHT_BRACE_2() break case RIGHT_BRACE_N then opRIGHT_BRACE_N() break end switch
See for many, like RHS_SLICE, only one condition should enter the switch. However, for RHS_SUBS_*, all three of them enter and perform the same action. This is very valuable and in more complex situations (which I didn't choose here for space reasons), it saves a ton of time and makes things much clearer once you understand what a switch does. Please see the euphoria source code (both C and Euphoria code) for some pretty complex and valuable examples.
Jeremy
